1. FIELD OF THE INVENTION
The invention relates to formulations based on aqueous dispersions, which, in addition to water, essentially contain water-dispersible polyurethanes, metallisation activators and preferably also fillers.
These formulations are used for the pretreatment of various substrate surfaces, for example surfaces of plastics, for the purpose of subsequent metallisation in currentless metallisation baths.
Components of plastic which have been activated using these formulations are preferably employed for shielding from electromagnetic waves after metallisation has been carried out.
2. Description of the Related Art
It is known that polymeric materials must be pretreated before chemical and subsequent electroplating metallisation in order to achieve adequate adhesion of the metallic layer to the surface of the material. The pretreatment is mainly carried out by etching the polymer surface with chromic/sulfuric acids, which pollute the environment. However, the use of chromic/sulfuric acid, SO.sub.3 vapour or other oxidising agents is accompanied by a deterioration in the physical properties, such as the impact strength and the electrical surface resistance of the polymeric material. Traces of 6-valent chromium, which can rapidly lead to poisoning of the metal baths, moreover often cause trouble.
The known processes for the currentless metallisation of materials furthermore comprise several process stages and have the disadvantage that they cannot be used directly on all polymers. Chemical swelling or physical roughening must often additionally be carried out.
It has therefore already been proposed to activate the polymer surfaces very gently using organometallic catalysts (DE-A 3,560,257 and EP-A 81,129). Nevertheless, this progressive method is also not universally applicable. The use of solvents moreover often leads to stress corrosion cracking being caused in the injection moulded parts of the polymer which are under tensile or compressive stress.
Other processes, such as are described in U.S. Pat. Nos. 3,560,257 and 4,017,265 as well as DE-A 3,627,256, have the disadvantage that they require larger amounts of expensive noble metal activators.
Specific adhesion-promoting plastics coatings are furthermore known from DE-A 3,814,506. However, these must be activated in activation baths before their metallisation, which may lead to geometry-related foreign deposition in cases of partial metallisation.